diff --git a/action.yml b/action.yml
index 82f8ad1..f18d16b 100644
--- a/action.yml
+++ b/action.yml
@@ -10,6 +10,8 @@ inputs:
       Rust toolchain name.
 
       See https://github.com/rust-lang/rustup.rs#toolchain-specification
+
+      If this is not given, the action will try and install the version specified in the `rust-toolchain` file.
     required: false
   target:
     description: Target triple to install for this toolchain